Separation of components in a stream is useful in many industries and can typically be accomplished by physical separations and/or adsorptive separations. The physical separations may involve techniques that separate different states of components in the stream, such as separating gaseous phase from liquid phase and/or from solid phase. For example, a flash separation involves dropping the pressure of a stream and separating the stream into a primarily liquid stream and a primarily gas stream. The adsorptive separations may be based on the differences in equilibrium affinities of the various gas components (e.g., equilibrium separations) or on the differences in adsorption kinetics of gas components (e.g., kinetics separations). As an example, solvents or sorbents may be used to adsorb certain components, while allowing other components to be conducted away with the remaining stream. For gas separations, the separation techniques typically involve separation with sorbents, solvents, membranes and/or cryogenics.
By way of example, hydrocarbon fuels may be combusted to produce various compounds, which may be discharged with the exhaust gas to the atmosphere. In particular, certain references describe the handling of exhaust streams in combustion engines. For instance, U.S. Pat. No. 8,931,461 describes operating an engine system having a sensor coupled to an exhaust gas recirculation system in a motor vehicle. The reference describes a method having two operating conditions. During the first operating condition, at least some exhaust gas from an exhaust of the engine is directed through the exhaust gas recirculation system and past the sensor to an intake of the engine, and, during a second operating condition, at least some fresh air is directed through the exhaust gas recirculation system and past the sensor. In addition, U.S. Pat. No. 8,661,799 describes a configuration for an exhaust stream from an internal combustion engine that passes the exhaust stream through a treatment device arranged in the exhaust line, and a heat source and a heat sink arranged in separate branches of the exhaust line upstream of the treatment device. This is configuration, a device is used to split the exhaust stream into multiple paths to regular flow into a downstream system. Further, Intl. Patent Application Publication No. 2012/021061 describes a system for controlling exhaust gas temperature of an internal combustion engine having a combustion cycle frequency and being provided with an exhaust gas after-treatment device. In this system, air is provided upstream of the combustion chamber, which is used to control the temperature of the exhaust gas. While these references only relate to combustion engines, the references do not appear to address managing the exhaust gas temperature with the induction of air downstream of the combustion or even removing gas components from the exhaust stream.
To limit the gas components provided to the atmosphere, various exhaust treatment techniques and systems are utilized to remove specific components from the exhaust stream prior to discharge to the atmosphere. For example, engine and/or gas turbines may utilize exhaust treatment components and/or systems to remove certain gas components from the exhaust stream. However, the exhaust treating techniques do not typically perform adequately at or above certain temperatures and/or pressures. For example, exhaust treating techniques may have diminished performance if the exhaust stream exceeds a certain threshold temperature. Unfortunately, the threshold temperature may be below the normal temperature of the exhaust stream for certain processes, such as combustion processes.
To adjust the temperature of the exhaust stream, tempering air systems are utilized with exhaust treatment systems to reduce the temperature of the exhaust gas in the exhaust stream to a temperature below the threshold temperature prior to the inlet to the exhaust treating system. The tempering air systems typically utilize fans or blowers to force air into the exhaust system. The forced air is cooler than the exhaust gas in the exhaust stream and is used to dilute the exhaust gas and lower the temperature of the resulting stream. The use of fans and blowers adds complexity to the overall system, are relatively complex to operate and expensive to install and maintain.
For example, certain references describe the handling of exhaust streams in combustion processes. In particular, U.S. Pat. No. 8,728,412 describes a method for reducing the emissions from combustion gases produced during a combustion process. The method includes injecting a hydrocarbon-based reducing agent into the combustion stream, which includes oxides of nitrogen. Then, the combustion or exhaust stream is directed through a selective catalyst reduction (SCR) system to remove oxides of nitrogen from the combustion stream. While the method describes using fans, pumps or flow control equipment as one approach to lower the temperature of the combustion stream, the references indicates that a preferred approach is to use a fast mixing techniques to reduce reducing agent residence time. In addition, U.S. Patent Application Publication No. 2013/074482 describes a method to extract hot exhaust gas from the exhaust stream, which is subsequently used to vaporize aqueous reactive reagents or to provide a heated air process gas mixture. In this method, the reference does not force air into an exhaust system to reduce the temperature, but the exhaust gas is removed from the exhaust stream for treatment.
Accordingly, there remains a need in the industry for apparatus, methods, and systems that provided an enhancements to manage exhaust streams. The present techniques overcomes the drawbacks of conventional tempering air approaches by cooling the exhaust gas in the exhaust stream without fans and blowers (e.g., relying solely on pressure differentials to provide a cooling stream). This present techniques provide a lower capital investment, much smaller equipment foot-print, and lower complexity of the tempering air system, compared to conventional approaches.